Receiver detector control



May 14, 1935. I D. GRIMEs 2,000,945

f RECEIIVFR DETECTOR CONTROL Filed June l2, 1951 lnnxnnl INVENTOR DAVID GNMES ATTORNEY Patented May 14, V1935 s Y s man; 1

s .2,000,945V RECEIVER DETECTOR ooN'moLul Y David ,Grimsgnangah staten Island, N. y., Y assignor to 'Radio` Corpora on' Aniericag'a' j corporation of'Delawarej i v )Y Y Y VApplication June,A 12, 1931, Serial N ,54

, xlwllaims..A 101.2515201 c,

"My present inventionv relates toA radio receivers, cathodecircuit of oneof the intermediate ampli-r and more particularly to a method of, and meansV .ext-"tubes'for` controllingzthe rvvolume ofthe set, for, regulating the seconddetectorof a .superandonefrormore; powertubesy-a compensationV heterodyne receiver. c f .f circuit in :thegridfcathodecircuit ofpsaidinter- Experience with lassuperheterodyne receiver of mediate tube to' reduceithe. intermediate ampliii'YK 5 Y awell-known type has disclosedthejactthat cationwhen the signalslon'said intermediate tube 1 there exists a limiting overloadingspoint for1the become 4strong enoughf-,to2 overload` the secondV power tube, or tubes, of the receiver, after ,whichV` detector. y v j point variationof the volume;contro1zinstrumen="v A,Still anotherimporitantobject of the presentA tality towardsV its maximum settingresultsfin `aA invention is to provide in a radio receiverhinclud'- 10:

decrease Vin volume, or stated diiTerentlyfin/any inga radiofrequency ampliier,` a detector and apparent de-tuning ofthe Vreceivenfln other an Vaudio frequency'amplifier,,theidetector being words, it has been found,.,for a type yofrssuper- [designed to overloadsubsequentto the audio am heterodynereceiver Vwhichincludes the usual lo- 'plier Iorroptimum roperating eiiciency,` an -arr cal oscillator, signal circuit, frequencycchanger rangementior rsubstantiallyreducing said de- 15 Y tube, intermediate frequencyamplifier tubes andz. tectorfoverload immediately after; the ,detector second detector, that as the volumecontrolagency overloads,` s, 1 y; Y.

isV increased up to a certain point of radiofre'f LAnd still otheriobjects ofthe present invention quency input, the `loudspeaker output increases are to improve generally the efficiency of, radio and distortion increases at powertube' overload, receivers,-and to particularly provide va detector 20 and that as the volume control device which regun overload control which isfeflicient in operation. lates the radio frequency gain is still further -inl- L'The novelfeatures which *Il believe to'be=char; creased beyond this point the output ofthe reacteristic of, my ginvention rkare lset forth ingI'Jar-xv ceiverY drops appreciably, and causes confusion ticularity inthe'appendedrclaims, 'the' invention s in volume control and tuning operations;l Y itself,h`owever, as,to/both'its'organization andV 25` This phenomenon may be attributed tothe sec-` method of `operation ,will best be understood by Y ond detector tube. fItrwas found that the control: reference to the `following description taken s electrode of the said tube became positive on connection withV thedrawing in whichl; have strong signals, thus'drawing current; u indicated diagrammatically-gone organization Now, I have discovered a methodV o1anclv de: wherebymy inventionmaybe carried into effect, 30 vised means for, alleviating the aforementioned, v vIn, the drawing, f a diiiculty in receivers, andsuperheterodyne,,fref-A Fig. 'f1 graphically .illustrates-the operationof ceivers specifically, by utilizing acompensating. a superheterodynereceiver,as shown-,in Fig. 4, device lin the control electrode circuit of thelast with,` and without; .thepresent invention emintermediate frequencyarnpliertube so'that' -bodied-insaid-receiver, f 5,; shortlygafter the second detector has'foverloaded l1'ig.,2-isga graphical representation `of the op' the control electrode of the said intermediate erationg'of a superheterodyne receiver,as shown tube assumes a positive charge, thus building up inFigA, during ascertain grange offvolume con-1. a negative voltage in addition toits predeterf trol variation, l Y 5^ f' mined Ibias, and thereby reducing the intermei Fig.4 3-is a, graphicalrepresentation of'the 40 t diate gain with consequent mitigationl of secondl operation Aoit* the same receivenduringa succeed detector overload. i s, Y, ing ppltionofthe-volumeacontrol.variation, ,'Accordingly, it is one ofV the main objects Aof,v vFig.,4diagramma'ticallyj'showsa'superheteromy present invention to provide, a superdynereceiver embodying the presentpinvention. heterodyne jreceiveremployingat least one in-l Refen-lng; tol theV accompanying:drawingl in 45 s termediateY frequency amplier tube, asystem for which-like characters :of reference` indicate the n substantially reducingsecond detector4 overload same parts inthe different gures, there isshownVV in the, receiver afterthe power tubes have been in Fig.' 4 af'conventional,and.i1ve1l; known;rtypel overloaded, and when the'volume control instruof vsuperbeteroclyne; receiverY Sold extensivelyfforf mentality Ais still further increased.v f radio broadcastifreception.; 'I'hisreceiver `usu, 50,

Anotherimportant object'sof the prlesentjinven-VV ally comprises a grounded antenna.;system1-A, ;G, tion is,toprovidefin'a,superheterodyne receiver the input 1ofa radio `frequency amplifier,` being l' comprising a, signal circuit, a. local osc'sillator,` aA coupledffto they-grounc'led-antenna. ,Thesaid requency changer'device;anintermediate- Ire amplierds rcomfentionally-V represented, ,alidgas A quebcy amplier-includineqmeansin the grid-c is weil; known to those; skilled rumeni-neem@ 55 t UNITED STATESPATENTOFICE- 2. i 4 prises one, or more, tuned stages of radio frequency amplification, each stage embodying an electron discharge tube of the triode or screen grid type.

The variable condenser l conventionally represents the fact that the amplifier is tuned to a desired signal. The output of the tuned radio frequency amplifier is impressed upon a` frequency changer? device, .or a first detector, this device .being conventionally represented'.y The detector usually comprises a triode, or screen grid, tube, it being understood of course that the input circuit of this device mayjalso..-be.tuned' is not part of the present invention, and there-1 fore neednotfbe further. described in any furtherdetail. *f

The difference, orV intermediate, frequency, Y isv impressed upon theinputcimuit of the first intermediate frequency amplifier tube l. through a transformer coupling, asat'M, itbeing noted that the first tubeis 'ofthe screen grid type. TheV input circuit of the tubedfs maintained Xedly tuned, by means of a relativelyA fixed condenser 5, to the desired super-audible difference frequency. pacity v6,' provides thenecessary bias for the grid of `the tube 4; AThe .output lcircuit of the first intermediate amplifier tube ismaintainedmiedly tuned, by Va relatively. fixed capacity 5',to' the intermediate vfrequency, and .thev amplified intermediate frequency; :energy is impressed, through a put circuit. of Va second intermediate frequency amplifier tube 9..

The second intermediate amplifier tube.,1also,

hasr its inputA circuit 'flxedly tuned, 'by means 'of' a relatively fixed condenser I0, to the intermediate frequency, bias for being secured' by means of an arrangement i', 1', vsimilar to Vthat-shown in connection withA the tube 4. The tube 9 is of the/screen grid! type, and its output'circuit is preferably-also'maintained fixedly tuned, byfmeans of: a relatively fixed condenser I0 tothedesiredintermediate frequency.

The second-intermediateemplifier tube is followed by a second detector f tube, which tube may be of` the triode, or screen grid type;y the input of the seconddeteetor.- being. maintained fixedly tuned, -by Fa relativelyfixed condenser Il,

to the intermediate. frequency. TheV detected` intermediate frequency lenergy is,{ then,"ampli fled by `means of anyr well knownvtype of audio amplifier, the latterembodyi'ng-Lone, or .'more,

stages of audio frequency' amplification, and each stage embodying'an electron discharge tube. vThe last Yaudio tube, or power tube,` (which powerr stage' as iswell known 'to 'those sln'liedfirr` the art may, if desired, comprise a. pair of tubes ecn--V neeted in push-pull) is usually connected to any well known typeof utilizatic'mYrm'eans','suchy as a inaiiyrepresented, l

' frequency amplifier a `constant difference'frequency between A resistor I 4rsliunted by fa by-pass ca-V tol 'a' point transformerV coupling.y 8,v upon the in-- the grid-'ofthe tube 9 loudspeaker of the electromagnetic or electrodynamic type, or even head phones if desired.

It will be observed that the grid biasing resistor 1 in the grid-cathode circuit of the second intermediateV amplifier tube 9 is shown variable. It will be understood that the resistor 1 is adjustable in orderv to enable it to function as .tothe volume control instrumentality of the receiver.V Clearly, this is not essential since the gain control device may be disposed in any other stage, as the radio frequency amplifier.

' Obviously, by varying the magnitude of the resistor 1', the amount of negative bias impressed upon the grid of the tube 9 can be regulated, with the result that the gain of the intermediate A is controlled.

In Fig. 1, there is graphically shown a series of curves which represent the operation of the receiver shown in Fig.

4, with, and without, the present invention embodied therein. Curve B illustrates the relation between loudspeaker output and radio frequencyv input after the magnitude of the resistor 1' is varied between its minimum and maximum Values. 'As-the volume control (it will be understoodA hereinafter that the variable resistor 1' with its associated Volume 'control on the operating panel of' the' set isiincluded within the meaning volume control. device) is increased Vso as to produce a radio frequency input lVariation from point o to u, it is found that the loudspeaker output increases in a substantially linear manner,

as shownbetween points o and a on curve B.

- With the volume control fixed at somepoint below af. on Fig. 1, there is obtained the curve B', shown in Fig. 2', as the tuning control 3 is tuned through a station. In other words, assuming that the volume control resistorl' is adjusted which will yield a radio frequency input lying between pointsV o and a, variation of the tuning knob 3 `through any given station setting will produce the relation represented `by curve B Vbetween the loudspeaker output and thetiming condenser Variation. Y Of course, at the resonance point s, the volume and quality for any given station will bev best, due to the presence of both the carrier and side bands.

Referring again to Fig. 1, as the volume control fl is now increasedbetween points which willr yield` radio frequency inputs between lpoints aand b on curve B, it will be found that loudspeaker output and distortion both increase. The distortion is. denoted by the departure ofthe curve'from its linear path. The point a on curve B is the point at which the power tubes overload, or stated otherwise is the point at whichlthe'grid of Y 'a power tube draws' current. It has been Y found ina superheterodyne receiver of the type shown in Fig. 4, that this point X is 3 watts.

Now, as the volume control is still further varied so as to increase the radio frequency input,it is found that the loudspeaker output drops appreciably, and causes confusion in operation. This is represented on curve B in Fig. 1, by the portion of the curve between points'b and c. It

will be seenthat the loudspeaker outputbetween these two points takes a very appreciable drop, and that at the point c it rises very slowly.v rThe significance of l the phenomena Voccurring between points b ando, to the operator of the set, is graphically shown in Fig. 3. It may be stated new that at the point b lthe second detector overloads." Y

Fig. 3 shows the same relations as has been shown in connection `'with Fig. 2. v The curve of the term 2,060,594 5'5 i-eieiin Between tuning Jenn.' denser variation and loudspeaker output 'through w represents the any station, if line P, Q were'followed in"Fig.g1,f lsubsequent to point a. 5 I Thatiis, =lineP-,'Qrepre` sents an ideal'condition of no overload of second detectorV and thecurve `w` is analogous to the resonance curve `B' `shown in Fig. 2, thecurve w merely being am-Y plied, since' that is what control between points b and'c'the'k decrease in Vthe curve Bf in y t tuning instrumentality 3 to point t; with there-V that the volume .i tion that has maximum.V power tube output.'

' nected to the low potential sides operator as die-tuning. Believingthat loudspeaker output often*l interpretedby the Fig. 3, thev set operator shiftsthe sultthae there' lest n.11, side bends carryingy the low audio tones. On the other hand,"if theKV set` operator fdcesnot readjustv the'tuning device tov correct the apparent di-tuning, butfreduces'the volumecontrol, the loudspeaker output increases upwards along the` slope'btw'een points'c Aand bV inFig. `1, thus makingj it appear to the operator control is` Vworking backwards.4 ',Ihat, is Vtoy say, the operationof the volume controlwill appear still more confusing, .since ,it willr apparently (increase the output of vthe receiver ,when it should beV decreasinggit..

vIn spite *ofthe desirability of jdeferringdetector overload for maximum volume, and'quaiity until the power tubes Ve ,overladed,theconfusion in operation at detector overladjstillv ex ists, because the opera-tor may have inadvertently adjusted ,thev volume on his receiver tola posi- 'I'his trouble is 4caused by the grid of the' detect-4 tor tube running positive upon vstrong signals, the grid drawing current in such cases.4 `Insuperheterodyne receivers `where thereexists a large induct'ance'inV the input circuit of, the sec-V ondudete'ctor tube and asmall value of capacity, the circuit maintained tuned 'by the xed ,capacity H, for example, hasfa relatively high yim-.j pedance, withv the result that ythe ygrid-cathode l resistance of. the tube, as the 'grid runs positive,

acts as a serious load onthetuned ,circuit causing an appreciable drop in'radio frequency voltage on the Ygrid of detector tube. This drop is suiicientV to cause the change in loudspeakeroutput shownby that portion `of the` curve B, in Fig. 1, which lies between thefpoints b and c.

A method of eliminating this'dro'p in radio frequency voltage on the grid of the second detector tube comprises the "insertion of a compensation circuit in the grid circuit of the 9. This compensation circuit comprises a fixed capacity 20 having its high Vpotential side `conof the inductance and capacity in the grid-cathode circuit of the tube 9, the low potential side of the capacity 20 being grounded. A resistor 2| shunt with" the capacity v2U, and functions as a` leakage path.

As soon as the grid of tube 9 runs positive, the entire grid circuit builds up a negative voltage,

power ,tubeef' Itis to be noted that c, a double peak occurs which'y what appears to h im to be the set'is tunedlto alpoint .von

need beused in such a case.

preceding tube y intermediate ampliiier means in the grid circuit of said tube for inis connected in Vtive with strong signals.

in addition ft its "predetermined bias;Y thus' reducing: the amplification so as Vto materially re-s duce ithemfollowing detector overload.V An Vexameple of the `values of tin circuitfit being understood that these valvv ues arelmerelygivenbywayrof illustration, com-[ prises giving the capacity 20 a value of Vone micro# the elements in the compensa#V farad, and givingthe'resistor 2i avalueof 'onef halfl megohm".

j Nerrnai bias is supplied by the resistor 71'.. inA

detectorvoverload The operation of the receiver, when embodying the "presenti invention,

Fig. 1 by the ."curve A'r. 'I'his last curve clearlyY Y illustrates what happens when the compensation* circuit 20, '2i is inserted in thegrid circuit o'f-the intermediate "amplier tube 9.` Itis beis graphically .shown in 20 andresistor 2li As'soon as the grid beginsto assume lieved' obviousfromthe aforegoing explanation, and the Ygraphical representation in Fig. v1; that th'eutilization of thefcompensation circuit-in the' grid circuit of an intermediate amplifier' tube eifectively eliminates `the operating disadvantage graphically represented Ain Fig. ,3. i Ofcourse, the invention is not limited to-utilization inthe sec,- ond intermediate ampliiier tube, but may be used in the rst vintermediate tube as well.

- Furthermorathe'present invention isfnot lirn-V ited to-superheterodyne receivers.,V Broadly f s tat'ed,it applies to any radio t a radio frequency amplifier, a detector vand a succeeding audio amplifier.v For example, 'the `de tector maybe of the-,power detector typewc'irk-k ,i

ing 'into Ya single power audio amplifier` stage, such detector usuallyk having high ypotentialsV applied to the grid `and anode fthereoiwln such cases, it is, highly desirable to `have thedetector overload subsequent -to the power tube, the ar-v rangement hereinbefore described, erating with the radio ally of ya high gaimto diminish detector overload in the manner described.`

heterodyne receiver iny Fig. 4 may be ofthe power type, wherebyfonlyy a single power audiotube Whilel have indicated and described one` arrangement for carrying my invention intoeiect, i

it will be apparent to one skilled in the art that my linvention is by ,forthf in the appended claims.`

y What Izclainfi` is:

receiver 'employing l Ofxcourse', the 'second detector of the Vsuperl no means limited to the par#V .ticular organization,` shown and described, but

' 1,.,'In1- combinatidn lwitha superhetrodyne re-l y eeiver including an intermediate frequency am;` plier consisting of an electron discharge tube provided with a grid circuit intermediate Vfrequency, t circuit of said tube for biasing the grid of said tube, and additional 2. YIn combination with means in the cathodev v n a sulerheterodyne re. `ceivervincluding an intermediate irequencyampliler consisting of an electron discharge tube provided with al grid circuittuned vto a desired intermediate frequency, means inthe cathode circuit for biasing the grid, of said intermediate amplifier tube, and a compensation circuit in provided `with* a grid circuit tuned to a desired intermediate: frequency,-means in the cathode circuit Tof the tube for biasing the grid of said intermediate amplifier tube, and 'additional means including a capacity shunted by a resistor in the grid circuit of said tube` for increasing the bias onthe'g'rid when, surging positive with strong signals.. Y Y Y 4. In combination with a superheterodyne receiver'including an intermediatefrequency amplifier consisting of an electrondischarge tube provided -withfagridcircuit tuned'to a desired intermediate frequency, grid of saidqintermediate amplifier tube, and additional means in the grid circuit of said tube for increasing4 the bias on' the grid `when surging positive with strong signals,V said first rnamed biasing means .comprising avariableresistor in the gridecatliode circuit pf said tube. v

7 5. Incombinationwitha superheterodyne receiver including anintermediate frequency am-v plifier consisting of `an electron discharge tube provided with a gridvcircuit tuned toa desired intermediate frequency, -meansv'for-biasing the gridv of saidintermediate amplifier tube, anda compensation circuit in the gridcircuit of said tube for increasing. the bias on the grid when surging positive with strongfsgnal's, said first named biasing means sistor in the grid-cathodeA circuit of said tube.

(i.V Incombination vqitha superheterodyne receivermincluding an inteimediaterlfrequency am, plifierconsisting ofan'electron discharge tube provided with a grid circuit tuned to a desired intermediate frequency, means ,for biasing the gridofsaid intermediate'amplier tube, and additional-means including Aa. capacity shunted by a resistorfin the gridcirc'uitrof said tube for increasing the bias on the grid when surgingpositive with strong signals, said first 'named biasing means comprising a variable resistor Vin the grid-cathode circuit of said'tube.

7. In a receiver including a' detector .and pre. ceding amplifier tube, ain arrangement for alleviating detector overload comprising an accumulator circuit in the ygrid circuit ofthe preceding amplifier tube ,designed to acquire ya negative chargeA as signals sufficiently strongr to overload said detector. swing the gridfpotential of vsaid preceding tube positive. A f

'8. In combination, inA aradio. receiver, a radio frequency amplifier, a"d'etector, an audioV .amplier, said Vdetector being designed to overload subsequent t'o' said audio arriplifier;V and addiplification means for biasing the comprising, a variable rek tional means, ,'associatediwithvthe radio frequencyamplier operative tordecrease the amthereofrinv response to signals of an intensitywhichiwould overload the detector.

9. In a; superheterodyne `receiver of the type having-an audiofrequency amplifier adapted to overloadprior to the second detector thereof and an intermediate frequency amplifier-feeding into the second detector, Ythe method of preventing decrease in receiver volume caused by overloading of the said detector which includes kso adjusting the circuit constants of said intermediate frequency amplifier that the gain of the intermediate frequency amplifier is decreased solely in response to signalsv of vdetector overloading intensity. y. c Y

10, In a superheterodyne receiver, a second detector stage having circuit constants such that the receivervolume decreases when the detector is overloaded, an. audio frequency amplifier arranged to overload prior to overloading'of said detector, ,an intermediate Vfrequency amplifier preceding said detectorincluding ladjustable bias means for varyingk the amplification thereof, and additional ymeans electrically associated with the intermediate frequency amplifierV for varying the amplificationt reof yindependently `of said adjustable biasmeans in response to signals of an intensity which would overload the detector.

il. In a superheterodyne receiver,V a second detectorstage having circuit constants such that thereceiver volurnefdecreases when the detector is overloaded, an audio frequency amplifier arranged to overload prior to overloading of said detectoran .intermediate frequency amplifier preceding ,said detector including adjustable bias means for varying the amplification thereof, and additional means electrically associated with the intermediate frequency amplifier for varying the amplification thereof in a direction opposite tothat of said adjustable bias means in response to signals of an intensity which would overload the detector. l ,Y f

-l2. In a radio receiver o f the type having an audio Yfrequency amplier adapted to overload priorto the detector thereof, the method of preventing undesirable decrease in receiver output volume caused by overloading of the detector which includes 'so adjusting the efiiciency of the transmission of lsignals through the receiver prior to detection that 'said prior transmission will be automatically" decreased solely in response to signals of an intensity which would overload the detector.`

13.A method of preventing apparent de-tuning in a radio receiver, Which is caused by reproduction volume-decrease when the detector of the 'receiver overloadsV subsequent to the audio frequency amplifier, consisting in amplifying the signals prior to detection, and causing a decrease in the said Vsignal amplification solely vin response to signals of detector overloading intensity.

YDAvD GRn/nrs. 

